BCM
has taken great care to ensure the best possible performance and
interchangeability. However, due to the large operational range of 300
Blackout ammunition in the market place, BCM cannot guarantee function
will all ammunition types in all conditions. These barrels were designed to run with a carbine buffer with subsonic ammo and a H3 buffer with high velocity ammo.
Fine tuning may be required in limited instances based on ammo and buffer choices that work best for the desired application. BCM also
recommends running the Crane O-ring (provided with all BCM Bolt Carrier
Groups) over the extractor with 300 Blackout.